Academic literature on the topic 'Yarn/matrix interface'

The use of inorganic cement based composite systems, known as Fiber Reinforced Cementitious Matrix (FRCM), is a very promising technique for retrofitting and strengthening the existing masonry or concrete structures. The effectiveness of FRCM systems is strongly related to the interface bond between inorganic matrix and fabric reinforcement, and, since the major weakness is often located on this interface, the study of stress-transfer mechanisms between fibers and matrix becomes of fundamental importance.FRCM are usually reinforced with uni-directional or bi-directional fabrics consisting of multifilament yarns made of carbon, glass, basalt or PBO fibers, disposed along two orthogonal directions. The difficulty of the mortar to penetrate within the filaments that constitute the fabric yarns and the consequent non-homogeneous stress distribution through the yarn cross section makes difficult to access the characterization of the composite material. The use of polymer coatings on the fibers surface showed to enhance the bond strength of the interface between fibers and mortar and, as a consequence, to improve the mechanical performance of the composite. The coating does not allow the mortar to penetrate within the filaments while is able to improve the bond between the two materials and to increase the shear stress transfer capacity at the interface.An experimental session of several pull out tests on carbon yarns embedded in a cementitious matrix was carried out. Different embedded lengths have been analyzed, equal to 20, 30 and 50 mm. The carbon yarns object of this study were pre-impregnated with a flexible epoxy resin enhanced with a thin layer of quartz sand applied on the surface.A variational model was proposed to evaluate the pull-out behaviour and failure mechanisms of the system and to compare numerical results to the experimental outcomes. Evolution of fracture in the yarn-matrix system is determined by solving an incremental energy minimization problem, acting on an energy functional which account for brittle failure of matrix and yarn, and for debonding at the yarn-matrix interface. The model was able to accurately describe the three phases of the pull-out mechanism, depending on the embedded length.

Interior fibers in yarns of plain woven carbon fiber-reinforced composite are distributed randomly, which further influences the mechanical properties of yarns. To explore the stochastic nature of fibers’ distribution in yarn and its effect on the properties of yarn, this study proposes a new perturbation algorithm named Sequential Random Perturbation algorithm to reconstruct the microstructure of randomly distributed fibers, based on which representative volume element micromechanical models consisting of three phases to accurately predict the mechanical properties of yarn are established. The algorithm is based on successive smart perturbations of fibers to gain microstructures of arbitrary volume fraction, and statistical study shows that the algorithm is in good agreement with experimental results. Finally, representative volume element models are simulated to predict the whole mechanical properties of composite yarns to reflect the failure mechanisms and microstructure–property relations. The randomness of fiber distribution has some degree of influence on mechanical properties of yarn, especially strength responses. The failures under axial tension and compression are dominated by fiber breakage, while under transverse and shear loading conditions, the failures are mostly decided by interface debonding and matrix damage.

The mechanics of damage of fiber composite sheets has been reviewed, including cases where the analytical models have been compared to experiments. The emphasis has been on the micromechanics approach, where equilibrium of the constituents of the composite lead to appropriate equations for determining stress distributions. The damage mechanisms that have been treated include fiber breaks, matrix cracking (splitting), and debonding at the fiber/matrix interface. Effects of matrix yielding, hybrid composites, the hybrid effect, and thermal response have also been discussed. The usefulness of the shear lag model (SLM) in both stress and fracture considerations is clearly exhibited by the results in the literature. Work on damage growth in uncoated woven fabrics has also been reviewed, together with its importance in Army applications. In the study of the localized mechanics of woven fabrics near damage sites (eg, yarn breaks), the important deformation mechanisms include crimp interchange between yarns, yarn slipping, and yarn rotation. Growth of slit-like damage as a progression of yarn breaks is reviewed. The structure of the equations in the analytical models is similar to the SLM, and a parameter appears which can be used to compare fabrics as to their damage tolerance. This review article includes 117 references.

In the past decade, natural fibre composites with thermoplastic matrices had attracted many composites manufactures for the superiority of lightweight and low-cost. A major challenge for natural fibre composites was to achieve high mechanical performance at a competitive price. Composites constructed from yarn and fabric structure preforms were better than composites made from random nonwoven mats. However, the twist structure of conventional ring spun yarns prevented the full utilization of fibre mechanical properties in the final composites. In this paper, the wrapped yarns were produced by wrap spun method with flax and polypropylene (PP), in which all flax fibres were twistless, then woven to be fabric preforms. The PP fibres served as a carrier for flax fibres during processing and became the polymer matrix in the final composites. The homogenous distribution of fibre and thermoplastic matrix in preforms could be achieved before hot pressing, so that not lead to impregnate difficultly, and prevented damage to the reinforced nature fibres during processing. Composites made from the wrapped yarn demonstrated significant tensile and peeling properties. The fabric structures (include plain, twill, and basket weave) and yarn tensile orientation (in 0°, 90°, 45°), had great influence on tensile strength and elongation of preforms. The cavity thickness of hot pressing mould had different influence on the tensile strength and peeling strength of thermoplastic composites, and the mechanical properties were superior when the thickness was 0.8-1.2 mm. The microstructure of thermoplastic composites showed uniform infiltration between layers, and had good bonding interface between flax fibre and PP matrix in composites.

In order to understand the impregnation mechanism of a yarn by a cementitious matrix and its influence on the mechanical properties of a yarn/cement composite, pull-out tests have been performed on samples of yarn/cement. Two embedded lengths for the yarn and different rheological and mechanical properties for the matrix were tested. Two pull-out modes were distinguished according to the compressive strength of matrices. For matrices with a compressive strength between 60 and 70 MPa the pull-out mode is characterized by a behaviour close to the tensile behaviour of the yarn, with maximum load values reaching approximately 60% of the tensile maximum load because of filaments damages. For matrices with compressive strength inferior to 60 MPa, the pull-out mode exhibits a residual phase linked to a slippage and an extraction of a variable number of filaments, with lower maximum load values than the first pull-out mode. After pull-out test, for some samples with filaments extraction, an innovative method based on a double impregnation with resin enables to visualize the yarn/matrix interface and identify the level of impregnation of the filaments by using confocal microscopy. It is concluded that this level of impregnation has a direct influence on the mechanical behaviour of the embedded yarn, except for the slippage and extraction phase, but the rheological properties of the matrix has no significant influence on this impregnation.

This paper investigates the tensile properties of 3D orthogonal woven carbon fiber composites with tilted binder by experiment and simulation. The tensile failure strain and fracture mode of this composite show distinguished discrepancy with idealized 3D orthogonal woven composites experimentally. In order to explain this specific failure mechanism, a unit cell finite element model incorporated with damage models of constituents is established to reproduce the damage initiation and propagation of 3D orthogonal woven composites with tilted binder during tensile test. A three-dimensional failure criterion based on Hashin's criterion and Pinho's criterion is utilized to describe the progressive damage of yarns, while the non-linear behavior of the matrix is predicted by Drucker-Prager yield criterion. Besides, a traction-separation law is applied to predict the damage of yarn-matrix interface. The proposed unit cell model is correlated and validated by global stress–strain curves, DIC full-field strain distributions and modulus history curve. The damage evolution process of 3D orthogonal woven carbon fiber composites with tilted binder, including fiber tow failure, matrix cracking, and interfacial debonding, is recorded and investigated by the modulus history curve from simulation.

The micro mechanisms of flexure damage at the notch tip in a three-dimensionally braided carbon/carbon composite (3D–C/C) were investigated in real-time through a Scanning Electron Microscopy. It was found that the damage was nucleated in the fibre bundle/matrix interface around the notch tip. The different damage modes were found in different directions of the 3D–C/C. The x-directional flexural specimens seem to be insensitive to the pre-notch while the z-directional flexural specimens seem to be sensitive to the pre-notch. Fibre yarns acted as an obstacle to crack propagation and it was necessary to increase the load to propagate the crack through the adjacent fibre yarn. Comparing with the x-directional flexural specimens, the forces could be better transmitted in z-directional flexural specimens because the fibres of z-direction bundles can tightly adjoin to each other.

The synthetic fibres have created some issues including risk of inhalation during fabrication process, renewability, biodegradability, and recyclability in composites industry. The usage of biocomposites as a replacement to synthetic fibres is beginning to be widespread. However, it is noted that lesser attention has been devoted to evaluating the mechanical properties of woven kenaf composites at various woven and stacked layer orientation. Thus, the research objective is to identify the effect of woven and stacked layer orientation on tensile and flexural properties of kenaf composites. Two types of fibre orientation are employed; type A contains a higher yarn density and type B contains a low yarn density. The tensile and flexural tests are conducted to analyze the mechanical properties of woven kenaf fibre composites and compare them to random chopped kenaf composites. The fracture interface between fibre and matrix epoxy is further investigated via scanning electron microscope. Type A kenaf improved up to 199% and 177% as compared to random chopped kenaf for flexural strength and tensile strength, respectively. Scanning electron microscopy analysis shows that resin matrix is properly induced into kenaf fibre gap hence giving additional strength to woven kenaf as compared to random chopped kenaf.

This paper focuses on two experimental methods that give indicators linked to the impregnation level of the yarn / matrix interface, in the case of Textile Reinforced Concrete (TRC). These methods have been tested on three different glass yarns laid in a cementitious matrix, with three different impregnation levels resulting from the manufacturing process. The first method (comparative mercury intrusion porosity test) is based on the evaluation by mercury intrusion porosity of the pores volume associated to the porosity inside and near the yarn. The second method (flow test) consists in measuring the flow rate of water along the yarn, with imposed flow conditions. The physical parameters measured by these two methods are both related to the pore size and to the porosity of the yarn / matrix interface. The results of the two methods are discussed and drawn in parallel to a qualitative characterization of the yarn matrix interface made by scanning electron microscopy. As a result, the connection between the results of the two methods and the SEM characterization is studied. It is shown how these methods can participate to characterize the yarn impregnation. Limitations of the methods are also discussed.

Cette étude porte sur l’analyse de l’influence de l’eau sur des composites chanvre/époxy. Deux résines ont été utilisées, l’une 100 % pétrochimique (Epolam) et l’autre partiellement bio-sourcée (Greenpoxy). L’absorption d’eau d’éprouvettes de composites tissés a d’abord été suivie par des mesures gravimétriques. Les résultats ont mis en évidence une cinétique d’absorption de type Langmuir dépendant de plusieurs paramètres (types de résine, de fibres et de tissu, fraction volumique de fibres et épaisseur). Des essais de DMA et DSC sur les résines ont montré un effet plastifiant de l’eau ainsi qu’une modification irréversible de leurs propriétés après le vieillissement hydrique. Des observations microscopiques réalisées sur le composite et à l’échelle du fil ont permis de détecter que des fissures entre les fibres de chanvre et la matrice époxy apparaissent et se développent dès le début de la désorption. De surcroît, des observations en photoélasticimétrie ont montré une réorganisation des contraintes internes irréversible due à ces endommagements. Des essais de traction quasi-statiques ont ensuite été réalisés sur des composites tissés et sur les résines seules. Le vieillissement hydrique modifie les grandeurs mécaniques ainsi que l’évolution des endommagements, suivie par émission acoustique et tomographie X.Pour mieux appréhender le comportement de l’interface fil/matrice, différents tests ont été développés sur des éprouvettes monofilamentaires spécifiques dans lesquelles le fil est orienté à 45° ou 90° par rapport à l’axe de sollicitation. Tout d’abord, des tests de nanoindentation ont été effectués de manière à mesurer in situ les propriétés de chaque constituant des composites avant et après vieillissement hydrique. Un second type de test basé sur le principe du choc laser a été utilisé pour déterminer la qualité de l’adhérence entre le fil et la résine. Enfin, des essais de traction sur micromachine sous microscope optique ont été mis au point dans le but de mesurer les champs de déformations par corrélation d’images. Les résultats ont démontré que les déformations locales sont plus importantes après un vieillissement hydrique et que ce phénomène est plus accentué dans le chanvre/Greenpoxy que dans le chanvre/Epolam. Le développement d’un modèle numérique simplifié a permis d’approcher la loi de comportement locale des différents constituants du composite et d’étudier l’évolution des modules après vieillissement
This study deals with the analysis of the influence of water on hemp/epoxy composites. Two resins have been used, one being 100 % petrochemical (Epolam) and the other one partially bio-based (Greenpoxy). The water absorption of the woven composites have been measured with gravimetric analyses. The results showed a Langmuir-type absorption, and depends on several parameters (type of resin, fibres and fabric, fibre ratio and thickness). DMA and DSC tests realised on resins showed the plasticizing effect of water and an irreversible modification of their properties after the water ageing. Microscopic observations of the composite at the yarn scale helped to detect that cracks between hemp fibres and epoxy matrix appear and develop right from the start of the desorption. Moreover, observations by photoelasticimetry showed an irreversible reorganisation of internal stresses due to this damage. Next, quasi-static tensile tests have been performed on woven composites and resins. The water ageing has modified the mechanical properties of the materials as well as the evolution of damage, which has been studied by acoustic emission and X-ray tomography.For a better understanding of the yarn/matrix interface behaviour, different tests have been developed with specific single yarn composites, in which the yarn is oriented at 45° or 90° in regard to the main axis of the specimen. First, nanoindentation tests have been performed, to measure the properties in situ of each component of the composites before and after water ageing. A second type of tests, based on the laser shock wave method, has been used to determine the quality of adhesion between the yarn and the resin. Finally, tensile tests on a micromachine under an optical microscope have been developed with the aim of measuring strain fields by digital image correlation. The results demonstrated that local strains are higher after a water ageing and that this phenomenon is more pronounced in the hemp/Greenpoxy than in the hemp/Epolam. The development of a finite element model led to estimate the local constitutive law of the different components of the composites and to study the evolution of the modulus after the ageing

Cette recherche porte sur les fils multifilamentaires de verre utilisés pour renforcer les matériaux à base de ciment. Elle est focalisée sur les interactions mécaniques de ce type de fils, constitués d'un assemblage de milliers de filaments micrométriques, avec un micro-béton et sur le rôle spécifique de l'imprégnation du fil par cette matrice cimentaire. Trois pré-conditionnements des fils ont été employés lors de la fabrication des éprouvettes afin de moduler les conditions d'imprégnation par la matrice cimentaire. L'imprégnation de 5 fils multi-filamentaires par la matrice cimentaire a été caractérisée et les paramètres d'imprégnation ont été définis en s'appuyant sur des observations MEB, ainsi que des essais de porosimétrie au mercure et des essais spécifiques d'écoulement le long du fil enrobé. Des essais classiques d'arrachement de type pull-out ont été utilisés pour la caractérisation mécanique. L'analyse des liens entre les propriétés mécaniques et les paramètres d'imprégnation ont permis de mieux comprendre les micro-mécanismes d'interaction filaments / matrice cimentaire et d'expliquer le comportement macroscopique à l'arrachement
This research deals with multi-filaments glass yarns used as reinforcement of cement based materials. It focuses on the mechanical interactions of these yarns, made of thousands of micrometric filaments, with a micro-concrete and on the specific part of the impregnation of the yarn by the cementitious matrix. Modulated impregnation conditions of the yarns were obtained by using three different manufacturing processes for the samples preparation. The impregnation of 5 multi-filament yarns by the cementitious matrix has been characterized and physical parameters of impregnation were determined using SEM investigations, mercury intrusion porosity measurements and specific tests of flow all along the embedded yarn. Classical pull-out tests have been used for the mechanical characterisation. The study of the links between the mechanical properties and the physical parameters of impregnation allowed accessing a better understanding of the filaments / cementitious matrix interaction micro-mechanisms, and explaining the macroscopic pull-out behaviour

La prise de conscience mondiale des enjeux environnementaux a conduit à l’émergence de composites«verts», dans lesquels les fibres naturelles sont amenées à remplacer les fibres synthétiques. Ces nouveaux matériaux offrent des alternatives écologiques aux composites synthétiques traditionnels mais sont difficilement utilisables pour des applications semi-structurales ou structurales. Une solution possible à ce problème est le développement des composites hybrides, en combinant ensemble fibres naturelles et synthétiques. Dans ce cadre, l'objectif de cette étude était de développer des composites hybrides à base de fibres de basalte et de lin. Les composites hybrides ont été élaborés par moulage par infusion sous vide avec une matrice époxy. À des fins de comparaison,des composites 100% à fibres de lin et100%à fibres de basalte ont également été produits. Une caractérisation mécanique quasi-statique et dynamique amontré que l'hybridation permet d’obtenir un composite avec des propriétés mécaniques intermédiaires comparées à celles des composites à fibres de lin ou de basalte. Cependant, l’analyse approfondie des dommages a montré la nécessité d'optimiser la qualité d'adhésion de l'interface fibre/matrice afin d'accroître les performances mécaniques des composites hybrides obtenus. Pour cette raison, différents traitements de modification de surface ont été développés et étudiés pour les fibres de lin et de basalte. Un traitement physique par plasma (Plasma Enhanced Chemical Vapor Deposition) a été appliqué aux fibres de lin et de basalte. Les fibres de lin ont également été soumises à deux traitements chimiques utilisant des espèces enzymatiques et du CO2supercritique. Les effets des traitements sur la stabilité thermique, la morphologie et les propriétés mécaniques des fibres de lin et de basalte ont été étudiés. L’adhérence fibre/matrice a été analysée en réalisant des tests de fragmentation sur des composites monofilamentaires. La qualité de l'adhésion entre les fibres et les matrices époxy et vinylester a été évaluée en termes de longueur critique de fragment, de longueur de décohésion interfaciale et de résistance au cisaillement interfacial. La micto-tomographie haute résolution a été utilisée pour analyser les mécanismes d'endommagement lors des tests de fragmentation. Pour les deux types de fibres, les meilleurs résultat sont été obtenus grâce au traitement par plasma. Ce traitement a consisté à déposer un revêtement homogène de tétravinylsilane à la surface des fibres de basalte et de lin, ce qui a permis une augmentation significative de l’adhérence fibre/matrice, ouvrant ainsi la voie à la prochaine génération de composites hybrides plus respectueux de l’environnement et utilisables pour des applications semi-structurales
Global awareness of environmental issues has resulted in the emergence of “green” composites, in which natural fibres are used to replace synthetic ones. However, in semi-or structural applications, it can be inconvenient to use composites based on natural fibres. A possible solution to this problem is the development of hybrid composite materials, combining together plies of natural and synthetic fibres. In this framework, the aim of this research project was to develop basalt-flax fibre hybrid composites with a view to obtaining more environmentally friendly composites for semi-structural applications. Hybrid composites were produced through vacuum infusion molding with epoxy matrix.For comparison purposes, 100% flax fibre composites and 100% basalt fibre composites were also manufactured. A quasi-static and dynamic mechanical characterization showed that the hybridization allows the production of a composite with intermediate mechanical performances compared to those possessed by flax and basalt composites. However, the damage analysis has revealed the need to optimize the fibre/matrix interface adhesion quality, in order to increase the mechanical properties of the resulting hybrid composites. For this reason, different surface modification treatments have been specifically designed and investigated for flax and basalt fibres. Flax and basalt fibres were treated by the physical process of Plasma Enhanced Chemical Vapor Deposition. Flax fibres were also subjected to two chemical treatments using enzymatic species and supercritical CO2. The effects of the surface modification treatments on the thermal stability, morphology and mechanical properties of flax and basalt fibres have been investigated. The degree and extent of fibre/matrix adhesion were analyzed by micromechanical fragmentation tests on monofilament composites. The adhesion quality between fibres and both epoxy and vinylester matrices has been assessed in terms of critical fragment length, debonding length and interfacial shear strength. High-resolution μ-CT has been used to support the analysis of the damage mechanisms during fragmentation tests. For both flax and basalt fibres, the best results were obtained after the plasma polymer deposition process. This process was able to produce a homogeneous tetravinylsilane coating on the surface of basalt and flax fibres, which resulted in a significant increase in the fibre/matrix adhesion, thus paving the way for the next generation of more environmentally friendly hybrid composites for semi-structural applications

Fabric reinforced or textile composites are increasingly used in aerospace, automotive, naval and other applications. They are convenient material forms providing adequate stiffness and strength in many structures. In such applications they are subjected to three-dimensional states of stress coupled with hydro-thermal effects. Assuming that a composite material is a complex structure it is obvious that is hard to describe all its properties in terms of its parts properties. The properties of the composite depend not only on the properties of the components but on quality and nature of the interface between the components and its properties. As reinforcement two types of fiber fabric were used; first one is a simple type fabric of untwisted tows of carbon filaments while the second one is also simple type but as yarn and fill are used alternately untwisted tows of carbon and aramide filaments. There were some problems to be solved before molding: fabric stability during handling, cutting, imbuing the carbon and aramide tows are slipping one on each other leading to fabric defects; generally the epoxy systems do not adhere to the carbon fiber; in order to obtain a valuable material the nature of interface must be the same for polymer-carbon fiber and polymer aramide fiber. In order to solve these problems the two fabrics were covered (by spraying) with a thin film of PNB rubber. Into the rubber solution were also dispersed small amounts of clay (to create a better interface) and carbon black (to improve the electrical conductivity). The rubber presence solves the fabric stability problem; ensures the same type of interface between fibers and polymer matrix; ensures a more elastic interface between fibers and polymer matrix. This treatment induces modification on tensile behavior of fabrics. This study is about mechanical evaluation of such fabrics.

Generally hybrid composite material is with two or more reinforcements or matrixes. They are referred as hybrid matrix and fiber hybrid. Further it is also included hybrid interface using different materials state of the interface. Therefore high functionality which compensates the disadvantages of each other by a hybrid can be expected. At current study, additionally, various strengthening forms were obtained and spread to textile material with hybrid(s). For example, techniques used in the weft and warp fibers/yarns might be different in making a fabric. It will be referred to as intra-layer hybrid fabric. It means in making fabric. It means that different physical properties due to the loading direction in one layer, the mechanical properties unique variety can be expected. In this study, carbon/glass intra-hybrid woven fabric was used to fabricate fiber reinforced plastic (FRP) composite through hand lay-up method. Then, the investigation on the mechanical property and fracture behaviour was carried out. Tensile test combined with acoustic emission (AE) measurement was conducted in this research. Knee point stress was the main factor of initial damage which discussed with AE characteristics during mechanical test. Due to the difference of energy release from fracture between glass fiber and matrix, the fracture characteristics of composite could be monitored during the test through AE facility. Relation between bundle and cracks inside the materials was examined through optical microscope. Scanning electron microscope observation was also carried out to examine the fracture of materials after testing.